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The objectives of this research were to quantify tilapia yields for established
Pond Dynamics/Aquaculture Collaborative Research Support Program pond nutrient
input strategies under climatic, edaphic, and water quality conditions found in
Egypt and to compare these results to those obtained using traditional Egyptian
management practices. Five treatments, each replicated four times, were tested
in 0.1-ha earthen ponds. Treatments tested were: Traditional Egyptian,
Enhanced Egyptian, Feed Only, Fertilization then Feed, and
Chemical Fertilization. Ponds were stocked with 20,000 Oreochromis
niloticus/ha; mixed-sex fish were stocked in Egyptian treatments and
sex-reversed fish in all others. Experiment duration was 145 days.
Nile tilapia gross yield differed significantly among treatments and ranged
from 1,278 kg/ha (chemical fertilizer treatment) to 2,877 kg/ha (fertilization
then feed treatment). Wild tilapia (O. aureus, S. galilae,
T. zilli) invaded all ponds and contributed 81 to 686 kg/ha to total
tilapia yield treatment means. Thus, total tilapia yield ranged from 1,407 to
3,537 kg/ha and represented from 78% to 96% of gross fish yield. Gross fish
yields ranged from 1,526 to 4,074 kg/ha. Tilapia yields in the Traditional
Egyptian and Fertilizer then Feed treatments was significantly
greater than in the Chemical Fertilizer treatment. Tilapia are marketed
in Egypt by size class as follows: 1st class - 1 to 5 fish/kg; 2nd class - 6 to
12 fish/kg; 3rd class - 13 to 25 fish/kg; and, 4th class - 26 to 40 fish/kg.
Farm-gate price varies from LE. 7.85/kg 1st class tilapia to LE 1.75/kg 4th
class tilapia. Greater yields of 1st and 2nd class tilapia were obtained where
organic fertilization was used in combination with formulated feeds than where
chemical fertilization alone or formulated feed alone were used. Results
indicated that ponds stocked with young-of-year monosex tilapia and managed
according to the tested systems were feasible in Egypt. PD/A CRSP research designs have been based on use of Nile tilapia
(Oreochromis niloticus) as the test species because this species was
common to all research sites. In Egypt, Nile and blue (O. aureus)
tilapia, both good culture species, are endemic. The objective of this
experiment was to compare production characteristics and production economics
of O. niloticus and O. aureus reared in ponds managed under
two different nutrient input regimes.
Eighteen 0.1-ha ponds at the Central Laboratory for Aquaculture Research,
Abbassa, Abou Hammad, Sharkia, Egypt, were used for this study using a
completely randomized design in 3 x 2 factorial arrangement, where factors
were tilapia species (Nile, blue, or co-stocked) and pond nutrient input regime
(chemical fertilization or fertilization then feed). Weekly applications of
nitrogen at 25 kg/ha and phosphorus to maintain an N:P ratio of 4:1 were
made in the Chemical Fertilizer treatment. In the Fertilizer then
Feed treatment, chicken litter was applied weekly at 1,000 kg dry
matter/ha for the first eight weeks followed by feed (25% protein commercial
fish feed) only. Ponds were stocked with sex-reversed tilapia fingerlings on
1 July 1994 at a stocking rate of 20,000 fingerlings/ha. Ponds are
scheduled to be harvested after completion of 150 days of grow-out.
Based on seine samples and estimated fish biomass, and assuming
20,000 fish/ha, the average mean individual fish weight after 83 days
of growth was calculated. The highest estimated biomass and average weight were
obtained in the Fertilizer then Feed treatment for O. niloticus
3,027 kg/ha and 151.4 g/fish, respectively. The co-stocked
Chemical Fertilizer treatment resulted in the lowest average weight/fish
(70.8) and in the lowest estimated biomass (1,415 kg/ha). Three simultaneous experiments were carried out to verify the pond management
software PONDCLASS, to regulate pond fertilization by total ammonia
concentration, and to evaluate the effect of raising the fish stocking rate
from 2 to 3/m2. The control was equal in all studies; ponds were
fertilized weekly with chicken litter at 250 kg dry matter/ha, urea to
maintain weekly total nitrogen input at 28 kg/ha, and diammonium phosphate
to supply 7 kg/ha total phosphorus input. Mean fish weight and production
of the control treatment were 15% and 28% greater, respectively, than PONDCLASS
means. Excessive nitrogen fertilization was recommended by PONDCLASS. Fish
production was thought to be limited by primary productivity, which in turn was
limited by carbon. The effectiveness of fertilizer input regulation by total
ammonia was inconclusive because of poor treatment management. Increasing the
tilapia stocking rate from 2 to 3/m2 had no significant affect on
fish production or water quality. The mean average fish weight of the control
treatment was 41% greater than the mean average weight of fish from the higher
density treatment. Stability of phytoplankton stocks and photosynthetic activity is important to
successful pond culture. Large phytoplankton stocks in fertilized ponds can be
unstable, and low total alkalinity (TA) can limit photosynthesis in ponds and
contribute to instability. It is important to understand management of TA
because it can change substantially during growth cycles in ponds, even when
soils are conditioned. This experiment documented temporal trends of TA in
15 ponds, and quantified the effect of interim additions of soluble
carbonate. For the CRSP Global Experiment, one of the five triplicated
treatments consisted of inputs management using the PONDCLASS decision-support
system software; another treatment consisted of regular inputs according to the
specified control protocol of Work Plan 7.
The results of this experiment are currently undergoing analysis; results
discussed here are preliminary. The five treatments produced no significant
differences in final mean individual fish weights, survival, or net yields
(P > 0.05, Single-factor ANOVA). Neither were there significant
treatment differences in mean concentrations of chlorophyll a or
daytime net primary production.
Management according to PONDCLASS produced yields with (numerically) greater
efficiency than did treatments involving regular weekly fertilizer inputs in
constant amounts, because similar yields were produced with less input. The net
yields for all ponds, extrapolated to units of t/ha/y, ranged from 3.3 to 6.5.
These are approximately double yields previously obtained at this site in the
same season (wet) during earlier experiments, but are substantially less than
yields obtained with these methods at a nearby site.
It is likely that rainfall affected the attempt to examine effects of soluble
carbonate inputs. During the first 50 days, when no rain fell, alkalinity
tended to decline during sampling intervals in all ponds, although
concentrations were effectively stabilized in ponds receiving carbonate
additions. After the first 50-day period the wet season began, and alkalinity
showed little decline in ponds of any treatment. Daytime net primary production
ranged (pond-by-pond) from -0.1 to 19.4 mg O2 l/d, with a mean of 7.0
for the experiment, equivalent to 2.0 g C/m/d. Higher values have been
observed on this site, particularly during seasons without rain and/or cloud
cover.
If completed analyses show that addition of soluble carbonate is effective in
stabilizing TA, such inputs can readily be incorporated into the PONDCLASS and
POND software systems and into transferred CRSP protocols. This will
effectively eliminate the potential for decreasing alkalinity due to
photosynthetically-mediated pH dynamics during production cycles in ponds,
leading to more stable blooms and production rates, and thus to more reliable
fish production protocols.
The Pond Dynamics/Aquaculture CRSP is funded under USAID Grant No. LAG-G-00-96-90015-00
and by
the participating US and Host Country institutions.
Questions for or about the Aquaculture CRSP? Comments about this site? Email ACRSP@oregonstate.edu.
Yield Characteristics of Two Species of Tilapia
under Two Different Pond Environments
Work Plan 7, Egypt Study 1B
Abstract
Nutrient Input Management by the Computer Program, PONDCLASS, and by Concentration of a Key Nutrient
Work Plan 7, Honduras Study 4A
Abstract
Management of Carbon Dioxide Balance for Stability of Total Alkalinity and
Phytoplankton Stocks in Fertilized
Fish Ponds
Work Plan 7, Thailand Study 6
Abstract
Disclaimers
